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Monday, December 25, 2017

Classification of Sewing Machines and Their Functions

Sewing is the process of stitch formation involving needle and thread. Sewing machines are textile machinery employed to stitch fabric or other material together with thread. Sewing machines were invented during the first industrial revolution to decrease the amount of manual sewing work performed in clothing companies.

Industrial sewing machines differentiate themselves from home sewing machines by varieties of bed and feed type, computerized functions and the possibility of integrating the work aids. While the bed types of sewing machines are important for optimized handling, the feed types enable uncompromised quality, computerization eliminates non-value-added elements and work aids de-skill the operation. Complete automation in sewing is limited due to difficulty in handling the limp dimensionally unstable material in 3D space. The cyclic sewing machines and sewing automats are primarily batch processes and concentrate on effective utilization of operators by deploying a lower person-to-machine ratio.

Classification of Sewing Machine:

Sewing machines are normally considered general working and from the perspective of its technical features sewing machines could be classified as shown in Figure-1.

1. Basic sewing machines comprise machines that sew with a lock stitch and multi-thread chain stitch. These are mainly intended for attaching garment components that are not exposed to high amounts of loads during wear using a lock stitch. Garment components that undergo higher load during wear require basic sewing machines that utilise multi-thread chain stitch.

2. Special sewing machines are proposed for specific technological operations and they can be categorised by (i) function, such as machines for pocket piping, sewing zips, knitted fabrics, etc. and (ii) stitch class and types except 301 and 401 stitch types, with blind stitch, zigzag stitch, for attaching pocket bags, etc.

3. Sewing automata are sophisticated specialised machines. The key features of these kinds of machines are its capability to perform automatic sewing when the fabric is positioned and the machine is actuated, cut the thread after sewing, release the fabric, etc.

4. Sewing systems are under advanced sewing machines. They have all the features of sewing automata and facilitate the automatic performances of two or more sub-operations.

5. Numerical-controlled sewing machines are machines where the fabric is guided automatically as in the case of sewing automata and sewing systems, but which follows a predetermined seam contour line. The numerical data are stored in the memory of a computer.

6. Robotic sewing systems have a multifunctional manipulator, where reprogramming and designing possibilities can be enabled for easy sewing.

Classification of sewing machines
Figure-1: Classification of sewing machines
Sewing Machine Classification Based on Its Bed Type:
The machine bed is the lower part of the machine and feed dog and loopers are positioned beneath it. Table-1 shows the various kinds of machine beds along with their uses.

The bed of a sewing machine is that part of the sewing machine on (or against) which the fabric rests while it is being sewn. The classification of sewing machine bed types or shape types is done based on the manner in which the fabric falls, behaves and travels with respect to the bed during the course of sewing, to enable easier movement of materials around the machine.

Table-1: Sewing machine classification based on its bed type

Sewing Machine
Features and Applications
Stitch Type
Flat-bed machine
Flat-bed sewing machine
A vast working space
permits a wide range of
sewing applications and is
utilised for all types of flat
sewing work.
Lock and chain stitch
Raised bed machine
Raised bed sewing machine
The machine bed is in the
form of a pedestal which
helps in assembling of
presewn parts. This is
specifically used for
attachment of accessories
and special attachments.
Lock and chain stitch
Post bed machine
Post bed sewing machine
It has a raised working
machine bed and is used
for stitching of three dimensional
such as shoes and bags.
Lock and chain stitch
Cylinder bed machine
Cylinder bed sewing machine
It has a horizontal
arm-shaped bed as well as
increased working height.
It is most suited for
sewing tubular
components like sleeves,
cuffs and trouser legs, and
can also be utilised for
button sewing and bar
Lock and chain stitch
Side bed machine or feed of the arm sewing machine
Side bed sewing machine
These are dedicated for
edge sewing and requires
a lesser working space
Chain and over-edge stitch

Classification of Sewing Machine Based on Machine Type:
The sewing machine classification based on the machine type is given in Table-2.

Table-2: Classification of sewing machine based on machine type

Machine Types
1. Lock stitch machine
Straight and zigzag seams
2. Chain stitch machine

3. Double chain stitch machine

4. Blind stitch machine
Blind stitch and hemming
5. Linking machine
Linking machine attaching trimming and
cuff of knitted fabrics.
6. Over-edge machine
Edge neatening and seam closing
7. Safety stitch machine
Safety stitching
8. Buttonhole machine
Specific sewing operation
9. Button sewing machine

10. Bar tack sewing machine

11. Profile sewer
Automatic, complex sewing operation
12. Pocket sewer

Different Feed Types in Industrial Sewing Machines:
Feed system, feed types and feed mechanisms are interchangeably used terminologies in different literature. The universally used feed system in sewing machines for fashion and commodity apparel manufacture is called drop oscillation feed or simply the drop feed from the bottom, which accounts for more than 90% of sewing machines installed in factories. The machine parts responsible for feeding from the bottom are drop oscillating feed dog and belt, while parts responsible for feeding from the top are needle, puller, rotary presser foot, walking (oscillating) toothed presser foot and belt. There are various feed types of sewing machine, they are given below.

Drop feed (bottom feed) sewing machine:
The three sewing machine parts that together constitute the drop-feed mechanism are presser foot, throat plate and feed dog. In a drop-feed system, the feed dog feeds the fabric from the bottom while the needle is up (Figure-2). As only the bottom ply is in contact with the teeth of the feed dog and the top ply is expected to slide (along with the bottom ply) below the presser foot with negligible friction, there is no positive binding force between both the plies.

Drop feed system
Figure-2: Drop feed system
Depending on the surface characteristics of fabric, the drop-feed system is subjected to severe inter-ply slippage (for slippery fabric or fabrics with very low frictional value) or negligible inter-ply slippage (for very high surface frictional value).

When the needle is up and stitch tightening is taking place, the feed dog is also up and the fabric is being supported from the top by the presser foot and at the bottom by the feed dog; therefore, there is no possibility of fabric being bulged by the tension of sewing thread, and drop feed is considered universally as the most suitable for sewing lightweight fabrics.

When two or more thicknesses of fabrics are being sewn, regardless of whether they are separate fabrics or folded sections of the same fabrics, the problem arises that friction between the bottom ply and the feed dog is greater than that between intervening plies. The tendency of the lower ply satisfactorily moving ahead with the feed dog and the upper ply being retarded by the presser foot is known as inter-ply shift, differential feeding pucker or just feeding pucker.

Needle feed (compound feed) sewing machine:
A compound feed is the combined simultaneous feed action of a needle feed and drop oscillation feed and is useful for sewing with a low inter-ply frictional co-efficient. In a compound feed system, the needle and feed dog together feed the fabric while the needle is down and inside the fabric (Figure-3). The needle moves in the direction of the stitch in a pendulum action (the tip of the needle is actually moving in an arc). As the fabric is transported by the feed dog from the bottom while needle is inside the fabric, there is controlled inter-ply slippage. As the needle movement arc length is small (0.083 inches for 12 SPI) and the fabric layer thickness being sewn is also negligible, the resultant inter-ply slippage is negligible to be noticed in sewn material.

Compound feed system
Figure-3: Compound feed system
However, when the needle is up and stitch tightening is taking place, the feed dog is down and fabric is not being supported from the bottom by the feed dog, and therefore there is a possibility of fabric being bulged/buckled by the tension of sewing thread in case there is not enough stiffness in the fabric plies. Although compound feed can control inter-ply slippage in thick material sewing (car seat cover, shoes, upholstery, luggage, etc.), it cannot be used for lightweight fabrics.

Compound feed is used to eliminate inter-ply slippage in multiple-ply sewing of thick materials, negotiating the corner of acute-angle-shaped components while top stitching at the edges. Generally double-needle lockstitch machines have a needlefeed system.

Unison feed sewing machine:
The feed dog, needle and presser foot all move together to feed the fabric while the needle has penetrated inside the fabric plies. The presser foot is split into two parts; one part has teeth beneath and moves in direction of feed while the other part moves only up and down and holds the fabric in between feed strokes, that is during stitch formation (Figure-4). Unison feed is used for sewing multiple plies of thick materials like tarpaulin fabric, polyvinyl chloride (PVC) and leather. It helps to do consistent sewing over cross-over seams of all types of thick materials without pitch errors (no stitch gathering or stitch elongation). It is used for sewing car seat covers, luggage, furniture using leather, PVC or other spongy thick fabrics, particularly in piping and binding-tape attachment processes.

Unison feed system
Figure-4: Unison feed system
Differential drop feed sewing machine:
Here two feed dogs are arranged in a series differential position in which the feed dog lengths follow one another in a straight line, one behind the needle and another in front of the needle (Figure-5). The rear feed dog (away from the operator) is called the main feed dog while the front feed dog (closer to the operator) is called the differential feed dog. When the differential feed dog takes longer or faster strokes than the main feed dog, the fabric will receive a linear compression force, and vice versa. The amount of feed by two feed dogs can be independently adjusted. Generally all overlock and/or cover stitch sewing machines have a differential feed system. In all areas where fabric is prone to stretch during sewing (diagonal and curved edges), differential feed ensures forced compression of fabric, which counterbalances the stretch and ensures correct shape and size of the seam.
Differential drop feed system
Figure-5: Differential drop feed system
Variable top and bottom feed:
One feeding foot at top and one feed dog below the throat plate feed the fabric plies together. The bottom of the feeding foot has a toothed surface. Feeding takes place while the needle is outside the fabric plies. Here, the top feed and bottom feed amounts can be independently adjusted to create inter-ply slackness or tension in the fabric being sewn. The presser foot is in two sections, one holding the fabric in position while the stitch is being formed and the other having teeth on the lower side and moving or walking in such a way that the top ply is taken along positively while the needle is out of the material (Figure-6). Positive control of the top ply allows for adjustments so that the fabric plies will either be fed through exactly together or, if required, the top ply is gathered into the bottom ply.

Variable top and bottom feed
Figure-6: Variable top and bottom feed
The feeding foot works before the needle to create a gather in the top ply, for example giving fullness while sleeve setting in the armhole of a blazer, and works behind the needle to create smooth seams, for example centring the back seam of blazer. The feed difference that can be created between top and bottom ply at best create fullness but cannot create visible gathers in one ply.

Variable top and bottom differential feed:
One feeding foot at the top and two feed dogs (like differential feed) below the throat plate feed the fabric plies together. The bottom of the feeding foot has teeth underneath. Feeding takes place while the needle is outside the fabric plies (Figure-7). This mechanism enables sewing two plies with the top ply gathering while the bottom ply remains flat. Here the feed difference that can be created between the top and bottom plies at the best creates visible gathers in one ply. This feed system is available with an overedging machine; a long panel join in skirts with a smooth flat seam without inter-ply slippage is possible, as well as a waistline join in a dress with a bottom ply gathered and sewn with a smaller bodice block.

Unison feed system
Figure-7: Variable top and bottom differential feed
Bottom feed and alternating drop feed:
One feeding foot at top and one feed dog below the throat plate moves in synchronisation to feed the fabric plies together. The bottom of the feeding foot has teeth beneath. Feeding takes place while the needle is outside the fabric plies. The presser moves up and down alternatively with the feeding foot. This feed system is used for difficult-to-feed materials and multilayered portions of medium and heavyweight material like synthetic leather products, vinyl coating products, leather products, rubber clothing and sponge clothing, with great precision. There is no irregular feed pitch due to positive feeding from both top and bottom plies.

X-feed sewing machine:
X-feed from Typical Corporation is characterised by needle feed and alternating drop feed. The feed dog is split into two independent feed dogs; the central one has a needle hole and acts like a needle feed, and the side one acts like a drop feed. During the first half of stitch length, the needle enters the material and also through the hole of the central feed dog (which is in ‘up’) and transports the fabric just like the compound feed mechanism; the side feed dog is below the throat plate level (Figure-8(a) and (b)).

Figure-8: X-feed system. (a) Central feed dog (gold colour) is up and transporting the fabric
while needle is down. (b) The side feed dog (sky blue colour) is up and transporting the material
while needle is up.
When the needle is leaving the material and going up, the central feed dog goes down and the side feed dog comes up and transports the material in the sewing direction just like the drop-feed mechanism. As the side feed dog is transporting the material in the sewing direction, the thread take-up lever is pulling the thread, an effect that stretches the stitch like on a puller machine. Due to the alternating movement of both feed dogs, material transport is continuous and calm in comparison to the intermittent feeding of drop feeding.

The X-feed claims to sew with 35% lower thread tension, which results in a flatter and pucker-free seam appearance, and the occurrence of ply slippage is also significantly lower in X-feed than in drop feed.

Cyclic Sewing Machines:
Cyclic sewing machines complete the sewing work in a short automatic cycle thus the name cycle, cyclic or automatic. In these machines, the needle moves only up and down to form the stitch, and the clamp feed moves the fabric horizontally (x-axis) or vertically (y-axis), creating the required shape. The movement of the clamp is controlled by a cam-follower mechanism or electronics. In an electronic machine, the movement of the cam is controlled by a microprocessor, and thus a different pattern and/or shape of tacks can be sewn easily by changing the program in the microprocessor.

Button-sewing machines:
These are either single chain-stitch (107 type) or lockstitch (304 type) machine heads where the fabric is placed over the cloth clamp and button is placed in the button clamp. Once the operator starts the machine the button clamp comes down and touches the cloth clamp; the button and cloth clamp together moves horizontally and vertically as per cam-follower or microprocessor movement and at the end of the cycle the thread is cut and the empty button clamp move up to the original position for sewing the next button.

Button with thread shank can be created by placing a spacing finger over the button during sewing (Figure-9), for shank button the button is clamped on its side and the needle passes alternately into the garment and then into the hole in the shank and into the garment
Thread shank can be created by placing a spacing finger over the button
Figure-9: Thread shank can be created by placing a spacing finger over the button
Buttonhole-sewing machines:
Buttonhole-sewing machines have either lockstitch zigzag (304 type) or double chainstitch zigzag (404) machine head where the fabric is placed over the cloth clamp. Once the operator starts the machine, the fabric-holding frame comes down and grips the fabric against the clamp and movement of the clamp starts. A buttonhole is formed by a series of zigzag stitches with varying degrees of needle throw-in synchronisation with xey axis clamp movement. The hole in the buttonhole is created by slashing/ cutting fabric either after sewing or before sewing. In an ordinary straight buttonhole (shirts and blouses), once the sewing cycle is complete the knife comes down to slash the centre of the buttonhole e called the cut-after mechanism. In knitwear, often buttonholes get distorted after washing; the appearance can be improved by doing stay stitching around the proposed cut area at the beginning of the sewing cycle. A stay stitch acts as reinforcement and stiffens the area around the cut.

Pattern-tacking machines:
Pattern-tacking machines have a lock stitch zigzag (304 type) machine head where the fabric is placed over the cloth clamp. The machine sews a pre-determined number of stitches in a particular shape or pattern using a combination of lockstitch and zigzag. The most common shape for cam-follower-driven machines is a small ‘bar’ or ‘I’, used to reinforce stress points like pocket openings and zip openings; thus the name of these machines was ‘bar-tacking machines’. The microprocessor-controlled machine can create any shape and therefore the name of the machine changed to the more generic pattern-tacking machine. Figure-10 shows sewing of a cross-tacking in a pattern-sewing machine. The cost of these machines depends on the maximum size of the tack and corresponding clamp size. Machines are available from approximately 6 cm2 to 4 m2 stitch area.

Cross-tacking in a pattern-sewing machine
Figure-10: Cross-tacking in a pattern-sewing machine
Classification of Computerized Sewing Machines:
Computerized sewing machines have small monitor displays for easier operation. A computer is used to control several different motors - precisely move the needle bar, the tensioning discs, the feed dog and other sewing machine parts. The computer controls all these fine controls, so it is possible to produce hundreds of various stitches. With the motor, the computer controls the right speed to move the needle bar up and down from side to side in a particular stitch pattern. We have published a complete article on computerized sewing machine. You can read below:

You may like: Classification of Computerized Sewing Machines

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